Vlasova E.V.1*, Golikov A.V.2,3, Lishchenko F.V.4,5, Dinh Y.H.T.5, Sabirov R.M.1† 2026. Reproductive characteristics of males of the spineless cuttlefish Sepiella inermis (Cephalopoda: Sepiida) from the waters of Vietnam // Invert. Zool. Vol.23. No.2: 304–324 [in English].
1 Department of Zoology, Kazan Federal University, Kremlyovskaya street 18, Kazan 420008 Russia.
2 Senckenberg am Meer, German Centre for Marine Biodiversity Research (DZMB), c/o Biozentrum Grindel, Martin-Luther-King-Platz 3, 20146 Hamburg, Germany.
3 Institute of Marine Ecosystem and Fishery Science, University of Hamburg, Große Elbstraße 133, 22767 Hamburg, Germany.
4 Laboratory for Ecology and Morphology of Marine Invertebrates, A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences, Leninsky prospect 33, Moscow 119071 Russia.
5 Coastal Branch of the Joint Vietnam-Russia Tropical Science and Technology Research Center, 30 Nguen Thien Thuat, Tan Tien, Nha Trang 650000 Vietnam.
* Corresponding author
†27th January 1958 – 28th June 2025.
E.V. Vlasova evlasova.uni@gmail.com ORCID: https://orcid.org/0000-0002-9536-7088
A.V. Golikov golikov.ksu@gmail.com ORCID: https://orcid.org/0000-0002-1596-2857
F.V. Lishchenko fedor-ln@yandex.ru ORCID: https://orcid.org/0000-0001-8340-346X
Y.H.T. Dinh yensinhthainhietdoi@gmail.com ORCID: https://orcid.org/0000-0002-2578-2630
R.M. Sabirov ORCID: https//orcid.org/0000-0001-5204-3027
doi: 10.15298/invertzool.23.2.07
ABSTRACT: Sepiella inermis is a widely distributed and commercially valuable species in southern Asia. Despite this fact, data on its reproductive biology are limited to information on sex ratio, monthly distribution of maturity stages, size at first maturity and gonadosomatic index. Therefore, the aim of this study is to provide data on aspects of the reproductive biology of males of S. inermis, that have not yet been described. A total of 51 mature males of S. inermis from the waters of Vietnam were studied. The testis, sperm duct, and all six spermatophoric glands showed negative allometric growth in relation to the mantle length. The number of spermatophores of S. inermis was 148–1787. No tentative spermatophores were found. The spermatophore’s length was 4.2–8.7 mm. The most distinctive morphological feature of the spermatophore was the structure of the cement body. The latter consisted of two parts. Oral part was striated at the anterior end and formed folds near the connection with the ejaculatory apparatus. The aboral part was cylindrical in shape and 1.5 times longer than the oral one. With increasing absolute size of the spermatophores, their attachment ability improved due to an increase in the size of the cement body. An increase in spermatophore length and in the size of the seminal reservoir was observed, which contributed to a higher sperm content in the spermatophore.
KEY WORDS: commercial invertebrate, reproductive strategy, male reproductive system, allometric growth, spermatophores, spermatophorogenesis.